Constraining the hydration state of the subducting mantle with converted seismic phases

在板块会聚的边界，水从地球表面被带走。它通过俯冲带进入地球内部，在地球系统的不同部分发挥着许多重要作用。虽然沉积物和海洋地壳中储存的水量已经通过近海钻探实验得到验证，但人们对岩石圈地幔中有多少水是俯冲的知之甚少。由于缺乏测量，问题就出现了：俯冲地幔中储存了多少水？在俯冲带之间的数量是如何变化的？控制地幔水合作用的因素是什么？对俯冲板块上方记录的地震图的分析表明，入射波场发生了P到S的转换，这表明在海洋地幔被认为是水合的同一深度处存在着物质对比。这种转换的性质暗示了该层的各向异性特征。它们表明，各向异性的一部分是继承的岩石圈的形成过程中的海底扩张，另一部分可能回到地幔水化的弯曲断裂俯冲前。转换信号可用于估计地震台站下方的海洋地幔岩石圈的含水量。我建议分析陆地地震仪记录的所谓各向异性地幔盖（AML）沿沿着所有会聚板块边界相对于其厚度和弹性张量的转换。我计划开发一种算法，用于搜索岩性，因此含水量，最适合如此发现的AML属性。随后将这一工作流程应用于全球台站组的结果是每个地震台站周边俯冲地幔的含水量。这一全球性的俯冲地幔水汇编可用于检验关于水供应在各种地球过程中所起作用的假设。控制地幔水化作用的因素可以被识别，全球俯冲水收支和速率可以更高的精度估计。

At convergent plate boundaries water is removed from the Earth's surface. It enters the interior of the planet through subduction zones, where it plays a number of important roles in different parts of the Earth System. While the amount of water stored in sediments and the oceanic crust has been validated through off-shore drilling experiments, little is known about how much is subducting inside the lithospheric mantle. As measurements are scarce the questions arise: How much water is stored in the subducting mantle? How does the amount vary between subduction zones? What are the factors that control mantle hydration?The analysis of seismograms that were recorded above subducting plates shows a P-to-S conversion of the incoming wave field that is indicative of a material contrast located approximately at the same depth to which the oceanic mantle is thought to be hydrated. The properties of this conversion hint at the anisotropic character of that layer. They show that anisotropy is to one part inherited from formation of the lithosphere during sea-floor spreading, and to another part likely goes back to hydration of the mantle during bend-faulting prior to subduction. The conversion signal can be used to estimate the water content of the oceanic mantle lithosphere beneath a seismic station.I propose to analyze the conversion of the so-called anisotropic mantle lid (AML) recorded at land seismometers along all convergent plate boundaries with respect to its the thickness and elastic tensor. I plan do develop an algorithm for searching the lithology, and hence water content, that best matches the so found AML properties. The result of the subsequent application of this workflow to a global station set is the water content of the subducting mantle in the perimeter of each seismic station. This global compilation of subducting mantle water can be used to test hypotheses about the role that water supply plays in a variety of Earth processes. Factors that control mantle hydration can be identified, and the global subducted water budget and rate can be estimated with higher accuracy.